1. Field of the Invention
The present invention relates to a semiconductor memory device with wirings having ensured cross-sections. The semiconductor device is used in a dynamic random-access memory (RAM), a static RAM, or a read-only memory (ROM).
2. Description of the Related Art
In a conventional dynamic RAM (DRAM), a plurality of parallel data lines are constituted by a single aluminum film.
With a structure wherein a plurality of data lines are formed by a wiring material such as a single aluminum film, the pitch of the plurality of data lines must be reduced to achieve a high-density DRAM having fine memory cells with a high packing density. As a result, the width of each of the data lines must be decreased.
Assume that the wiring pitch is 3.5 .mu.m. In this case, when the width of a contact pad is larger than the wiring width by, for example, 0.5 .mu.m, the wiring width is increased to 1.5 .mu.m and the wiring interval is accordingly 1.5 .mu.m. These values are given in a conventional 250-Kbit or 1-Mbit DRAM.
When the packing density of the DRAM is increased and the wiring pitch is decreased to 2.1 .mu.m to 1.5 .mu.m, the wiring width and the wiring interval must be decreased to about 0.8 .mu.m to 0.5 .mu.m under the condition wherein the same margin (i.e., 0.5 .mu.m larger than the wiring width) as described above is given to the contact pad.
In a very large-scale semiconductor memory device of a DRAM of which a structure of high concentration and high integration is required, with such a wiring structure, the wiring width is greatly decreased, the cross-sections of the wirings are greatly decreased, the wiring resistance is increased, and hence the electromigration effect is increased. Accordingly, the operation speed and the reliability of the semiconductor memory device are deteriorated.